Nasa engineers work on Spirit replica

A few months after it landed, Spirit's left front tyre began showing a problem by using much more energy than the others.

Here, Jet Propulsion Laboratory (JPL) engineers Eric Aguilar (left) and Joe Melko work in a sandbox to find a way around the problem. The wheel eventually died in 2006 but Nasa scientists were able to keep the rover rolling on five wheels by driving it backwards and devising easier ways to turn.

Patch of silica on Mars

On a positive note, the dead wheel dug up Martian soil that in turn led to Spirit's most impressive discovery — a patch of nearly pure silica. This was most likely caused by hot springs or steam vents.

Rocks on Mars

Five years after this image was taken by Spirit in 2005, Nasa scientists concluded that this area showed a past that was wet and non-acidic and could potentially sustain life as we know it.

The rocks were identified as magnesium iron carbonate with a concentration of carbonate 10 times that ever seen on Mars. According to the space agency, carbonates originate in wet, near-neutral conditions, but dissolve in acid.